HPA Nerf Blaster Modification

Hello! I have created an HPA nerf blaster modification. This is my first big nerf modification and I think it came out pretty well. I made this because I have seen similar things been made on Youtube and it inspired me to something similar, Unfortunately, I had to adopt a different system that is different from the ones I have seen, but I think it make it look cooler so I am okay with it. I also want to put out there that this can be dangerous and lead to injury, so do not run this at unsafe pressures. I am not responsible for injuries caused by this.

Firing System

3X Barbed hose fitting ¼”

3ft of rubber fuel line ¼”

2X barbed hose fitting ⅛”

Clippard MJVO-3 valve

Quick Exhaust Valve 1/4" opening on all ends

2X Air Hose Connector Plugs ¼”   1 female and 1 male threaded ends

Metal male to female 90 degree bend ¼”

Breach

½ inch copper pipe

Molding putty

Tank

PVC Primer

Heavy Duty PVC Cement

Teflon Tape

barbed brass hose connector ¼”

Male to female threaded 90 degree bend ¼”

Threaded metal tee ¼”

Mulitrange Brass pop safety valve ¼”

Metal nipple fitting ¼”

Metal reducer ¾” to ¼”

PVC Bushing 1-½” to ¾”

PVC Coupler 1-½”

7” of 1-½” PVC pipe

PVC end cap 1-½” 

First things first, the air tank. To start, you want to get your PVC 1 -½” to ¾” bushing and your 1-½” PVC coupler. After covering all of the needed surface area on both pieces with primer, you can apply the cement to the inside of the coupler and push the bushing into the the coupler. Make sure to twist the bushing as you are pushing it in so the cement evenly distributes itself. Then, take your 1-½” PVC pipe and cut 7” off of it. Take that 7 inch pipe and apply the primer to the other side of the coupler and one of the sides of the pipe. Then apply the cement to the inside of the coupler and push them together, make sure to twist it as well. Repeat this process with the endcap as well, applying the cement to all contact surfaces and applying the cement to the inside of the cap and twist it into place. 

Now you need to create the connection system for the tank. Take your male to female ¾” to ¼” metal fitting and screw it into the bushing of the pvc tank. Then take your ¼” threaded nipple and apply Teflon tape to one side of the nipple and screw it into the fitting until you can turn it anymore. Next, apply Teflon tape to the other side of the nipple and screw in the ¼” metal tee. Next screw your pressure relief valve into the far end of the tee and use a wrench to completely seal it. Now take one of your male to female 90 degree bends and thread it into the other open port of the tee. Make sure to thread it in enough that it is parallel to the brass safety valve or as close as you can get it. I find that applying a little extra Teflon tape can make the bend lock out at about the right angle. Then you just have to put a ¼” hose fitting into the female part of the bend.

Now the fun part, the firing mechanism. Take a ¼” hose fitting and an air hose connector plug (the far right module in the first picture) and thread them together. Next take your two ⅛” hose fittings and the MVJO-3 valve and thread those into the switch (See middle module on first picture) (An adjustable wrench is recommended to make these as tight as possible.). Now take your Quick Exhaust Valve and thread in one ¼” hose fitting in on side and on the other side thread in a hose connector plug. (This is just a spare part that I used so that the valve could be slid into the barrel easier). You will want to make cuts in the gun frame before you set up the hoses because it makes everything easier.

Now for one of the more stressful parts of the project. Cutting the shell to fit the components. Using a dremel is by far the best tool for this. I recommend taking a picture of the gun internals before you remove all the parts. Take out all of the internal components so you don’t risk damaging them. Note: for this project you will have to remove the stock and the stock mounts will be cut out in the process of this build. Try to line up the components how I did inside the blaster. When cutting out the shell, be very careful to not cut too much out, take your time on this step so that the components don’t move around while the blaster is closed Also keep in mind there is another side of the shell, so if you want everything to be centered you only have to cut the shell so that only half of the component is sticking out of the shell. Then start with the hose connector and hose fitting module and line it up to where you want it to stick out. Then cut. Next take your MVJO-3 valve and line the button up under the trigger like in the picture, then cut. Note: you are going to have to cut out some screw mounts for this to fit as well, the gun still screws together well so it's not a big deal. The hardest part to cut out is the valve, The back of the valve (not the hose fitting) should line up with the screw mounts located here (Red) There is a black sharpie mark I made to I knew where to put it at. Then you slowly cut out the frame going off of that point until you reach the point where you have to cut the hole through the blaster. I figured out where the hole was going to be and cut a line there, and turned the gun over and created a small square hole on the other side, then carefully shaved of the sides until the valve fit completely through. Then for the other side do everything the same but don’t cut a hole through the gun on the other side. I left all the components side the one side and would cut the other side until they fit together with the components inside.

For the hoses I had one long piece of fuel line. I put all the components into the blaster shell and held the hose up between the components and made marks on the hose to know here to cut them. If you want to add hose clamps as well, you can, but they aren't necessary. Once you make your cuts you can thread the hoses into place on all the parts. I recommend making the hose a little longer than needed for the space between the 2 valves so that the hose isn’t pulling down on the QEV (Quick Exhaust Valve).

The barrel and breech system are by far not the greatest, I had to make many compromises on the project in this area. I used a ½ copper pipe as the main barrel and I reused a part from the blaster (red) for the breech. Unfortunately The magazine doesn’t work with this design, and you will have to manually load it, which is annoying. There are many good tutorials on how to make a breech system so if you opt to do that you can disregard this part. First take your future barrel slide the the pipe into the end of the QEV valve (these should be in the gun for fit reasons) and then mark on the copper pipe the outside of the magazine entrance Then cut the pipe so that there is a small amount of pipe left (Picture 2) then take the bolt sled piece (Green) cut off the barrel/plunger piece so that there is a small nub on the end where it was attached and then glue the little barrel piece to that nub. You will want to glue it so that the end of the barrel piece is near the middle of the nub. There is a lot of line up check you have to do to make this work, because every situation is different so I would recommend putting the barrel in place and see if the spacing for the breech works before you glue it. I used hot glue because is was easy to work with, and it may take a couple tries, but you want to try to make this as straight and flat as possible. Once it is dry you can completely assemble the gun. I used putty here and there to hold things in place, I put putty around parts of the barrel to keep it from rotating and to stay in place.

There are a couple of modifications at had to make after the fact to fit everything in and run smoothly, on of these was the trigger, you will need to most likely sand this (Red) down so that it does get caught on the switch. Next you will have to sand this down (Green) so that the breech move smoother and doesn’t get caught.

Now, you blaster should look like picture 1. Now, take the other shell piece and screw it into place so that the blaster is fully closed up. Attach the barrel attachment and now it should look like picture 2. Take your last 90 degree bend and ¼” hose fitting and screw those together, then screw them on to the outlet of the QEV valve that is sticking out of the gun. Remember to use Teflon tape. Then I mounted the air tank to the bottom of the barrel using zip ties around the main portion of the air tank and between the tee and the fitting of the tank. The last part you need is the hose to connect it all. Take your remaining hose and mark how long it needs to be, use a little extra just in case, and them put it into the hose fittings. Next, if you want it to glow in the dark like mine does, you can get glow in the dark paint or gel and put that on there.

This is what the final product looked like, I am pretty proud of it since it is my first large scale nerf mod, and my first time messing with pneumatics. Overall, it works. It doesn't shoot very far because of the whole breech and barrel compromise I had to make. At around 80 psi I got the dart to go 70 feet and it works every time and doesn't fail so I am happy with that.